The present invention relates to lubricant compositions particularly for internal combustion engines. The lubricant contains a nitrogen-containing dispersant or TBN booster which provides a significant amount of the basicity of the composition.
Projected global engine emissions standards for the period up to 2010 and beyond will require significant changes in the formulations of crankcase oils, including crankcase oils for heavy duty diesel engines. There is, for instance, an emphasis on providing oils with significant reduction in sulfur, phosphorus, and sulfated ash (ASTM D-874.) However, such lower levels have serious impact on engine oils. Reduced ash levels, for examples, will necessitate a reduction in the amount of metallic detergent, which have been used to provide base to neutralize acidic fuel and lubricant degradation products. This neutralizing function is particularly important for use with extended oil drain intervals, where reduced detergent levels may jeopardize oil life.
Oil life may be extended by increasing the total base number (TBN, ASTM D-2896) of the oil. The challenge is to deliver TBN without adding ash or harming seal compatibility, particularly for Viton® fluorocarbon (fluoropolymer) seals, which is often a problem when basic nitrogen compounds are added. The present inventors have discovered that the addition of certain selected nitrogen-containing dispersants to lubricant formulations, especially low sulfur, low phosphorus, low ash diesel oil formulations can boost the TBN level of the lubricant without harming fluoropolymer seal compatibility or in some cases even improving fluoropolymer seal compatibility.
The lubricants of the present invention are useful for lubricating apparatus generally, but particularly for use as engine oils for internal combustion engines. These include passenger car engines, small engines, marine diesel engines, stationary gas engines, two-cycle and four-cycle engines, and engines fueled with gasoline, diesel fuel, organic fuels such as alcohol and hydrocarbon-alcohol mixtures, natural gas, and hydrogen, and sump-lubricated and fuel-lubricated engines. It is particularly suited for lubricating heavy duty diesel engines such as the type found in trucks. It is also suited for heavy duty diesel engines which are equipped with exhaust gas recirculation systems. Such systems may be used in efforts to reduce environmental emissions from such engines. Among the consequences of recirculating the exhaust gas through the engine are different soot structures and increased viscosity of the oil at lower soot levels, compared with engines without EGR. It is desirable that lubricating oils for such engines exhibit minimal viscosity increase, e.g., less than 12 mm2/sec (cSt) at a soot loading of 6%. Diesel engines with EGR may also experience higher loadings of acidic products of combustion, imparted to the lubricant from the exhaust gases, so lubricants with high TBN levels are often desirable to effect neutralization of such acids.